---
title: "Can you mix regular petrol and premium petrol?"
description: "Regular petrol and premium petrol: yes, this is fine. What actually happens, and what to do instead."
url: https://atoneplace.net/can-you-mix/petrol-grades/
site: "At One Place"
---

# Can you mix regular petrol and premium petrol?

**Regular petrol and Premium petrol: Yes, this is fine**

Yes. They blend, and the tank ends up somewhere between the two octane ratings.

## What actually happens

Octane rating is a measure of resistance to knock, and mixing two grades gives an intermediate rating in proportion. A car specified for premium running on a mixture will retard its ignition timing slightly and lose a little power; a car specified for regular gains nothing at all from premium. Diesel in a petrol tank, or the reverse, is an entirely different question and a serious one.

## What to do instead

Use whatever the fuel filler flap specifies. Higher octane than required buys nothing.

## Vehicle fluids

| Combination | Verdict | Why |
| --- | --- | --- |
| One engine coolant and a different coolant type | Do not | No — not across chemistries. The additives react and can gel. |
| DOT 3 brake fluid and dot 4 brake fluid | Fine | Yes. Both are glycol-based and fully miscible. |
| One engine oil and a different brand or grade | Fine | Yes. Any two oils meeting the same specification mix safely. |
| DOT 5 brake fluid and dot 4 brake fluid | Do not | No. DOT 5 is silicone and is not compatible with any glycol fluid. |

## Common questions

### Can you mix regular petrol and premium petrol?

Yes, this is fine. Yes. They blend, and the tank ends up somewhere between the two octane ratings.

### What happens if you do?

Octane rating is a measure of resistance to knock, and mixing two grades gives an intermediate rating in proportion. A car specified for premium running on a mixture will retard its ignition timing slightly and lose a little power; a car specified for regular gains nothing at all from premium. Diesel in a petrol tank, or the reverse, is an entirely different question and a serious one.

### What should I do instead?

Use whatever the fuel filler flap specifies. Higher octane than required buys nothing.

## Related pages

- [One engine coolant and a different coolant type](https://atoneplace.net/can-you-mix/engine-coolant-types/)
- [DOT 3 brake fluid and dot 4 brake fluid](https://atoneplace.net/can-you-mix/dot3-and-dot4-brake-fluid/)
- [One engine oil and a different brand or grade](https://atoneplace.net/can-you-mix/engine-oil-brands/)
- [DOT 5 brake fluid and dot 4 brake fluid](https://atoneplace.net/can-you-mix/dot5-and-dot4-brake-fluid/)
- [Bleach and ammonia](https://atoneplace.net/can-you-mix/bleach-and-ammonia/)
- [Bleach and vinegar](https://atoneplace.net/can-you-mix/bleach-and-vinegar/)
- [Bleach and toilet cleaner](https://atoneplace.net/can-you-mix/bleach-and-toilet-cleaner/)
- [Bleach and rubbing alcohol](https://atoneplace.net/can-you-mix/bleach-and-rubbing-alcohol/)
- [Hazard symbols](https://atoneplace.net/symbol/)

## Sources

- Official vendor product documentation — At One Place (/about/)